Do two water pickups. Preferably transom pickups. One will be dedicated to the engine with a mascerator type strainer. The second pickup will go to a mini mascerator type strainer. This way, the water will be cut off when the boat is off plane. This will prevent the fuel from condensing on the cooler. I would use a stock merc water pump with stock merc oil coolers. This way you can use preformed hoses and the merc brackets. When they are custom painted you get a nice clean installation. I know KE makes a multi-stage water pump, but has anybody ever really needed one? A stock waterpump is nice because you can get a impeller just about anywhere.